At the 2011 GreenBuild in Toronto, Jim Schuessler, ASLA, BNIM, and David Dods, URS Corporation, a dynamic landscape architect and engineer duo, outlined lessons learned from two years of research into stormwater management best practices in sites across Kansas City. Sampling results from rain gardens, bioswales, “treatment trains,” and other green infrastructure systems, they explained how collecting data and measuring results is key to determining what types of approaches are most effective and cost-efficient. Given more communities are integrating man-made stormwater management systems that mimic nature into the built environment, their research has value.
Dods said it’s important to “think like a raindrop.” In nature, rain evaporates, or hits trees, where it’s captured by leaves, and then rolls down trunks into the soil. There, it’s absorbed slowly into the soil and captured by plant root systems. In prairie systems, grass roots can go down 10-15 feet into the soil. Not only do the roots and soils capture water, they also remove pollutants. In nature, water and land connect: there’s a gradual change that “creates intimate connections.” In contrast, with urbanization, this process of natural water management has been broken. When water hits paved surfaces, it rushes right off, into stormwater drains, collecting toxic particulate and disolved building, lawn, and car waste in the process. Dods did an experiement on his roof and found from “roof to drain,” it took 1 minute 17 seconds for water to flow off his roof and parking lot into drains, leaving no time to filter out pollutants and capture excess water.
In four test sites across Kansas City, Dods and Schuessler used a range of high-tech gizmos to measure a range of ecological functions: A teledyne (ISCO) machine, which “looks like a keg,” was used to sample water flow every five minutes. Bubbles of air determine when water has entered the system, and this turns on the machine. Piezometers, or monitoring wells, are used to figure out how much water moves through a site. Rooftop tipping buckets (rain gauges) help the team figure out rainfall flow. Soil samples and soil moisture rates were also taken and measured to determine how the soil material changed.
The sites include a highly urban site at a downtown mission, which featured an infiltration basin; two locations at the headquarters of Applebee’s, with a rain garden and “treatment train,”; and another site at the University of Kansas, which included a rain garden and detention basin.
The downtown mission test site, which cost some $70,000 to design and build, had three sets of basins that move water through a level of steps. The idea is that each step will capture any overflow from the previous level. A combination of rocks, soils, and sands successfuly captured 1-inch of stormwater. But the team found that this was due in part to a subterranean basin found underneath the site. Schuessler said the lesson learned was that “soil and site characteristics have a huge impact on how a site functions.” It’s then important to do test pits to see what the conditions really are.
In the first site at Applebee’s Headquarters, overflow from the roofs were moved through to a set of rain gardens in plazas below. Four roof drains help distribute the water flow. The data said that the rain garden systems had “modest pollutant removal” results – some 50 percent of pollutants were removed through the system. However, they found that the rain gardens were under-sized and couldn’t hold 1-inch of run-off. Still, they found that “distributing flows instead of using one big pipe” was key to moving towards a system with greater ecological function.
The other site of the Applebee’s site was a “treatment train” designed to capture stormwater runoff from 15 acres of parking lots and clean water for the 5 acres of water in a nearby public retention basin. Sediment “forebays” included deep rock-covered sand filters that successfully removed many pollutants. “These sand sponges cleaned water before they moved towards the wetlands,” said Schuessler. U-shaped wetlands then create wildlife habitats, although, interestingly, they were designed to be geese-proof. As Dods explained, geese like water surrounded by turf grass so they can have a clear view and guard against the predators. The only issue: water fowl feces wreck havoc on water quality. As they explained, geese were negatively affecting water quality in the wetland — adding bacteria — before the grasses grew in. There were other issues with sediment entering the wetlands, but Schuessler explained this was due to other client work on site.
Lastly, University of Kansas’ site, which was designed by that university’s landscape architecture students, divided streams of water leaving the roof into 11 separate streams. Plants were added and placed based on their tolerance for water. “There were different moisture zones, creating a set of micro-ecosystems,” Dods explained. As a result, it took 1 hour and 20 minutes for water to move through the vegetated systems, being cleansed in the process.
Dods and Schuessler had 10 key takeaways, which resulted from their comprehensive data collection and measurement experiements:
1. Preserve existing landscapes. It’s easier to preserve than rebuild natural functions.
2. Development disturbs soils. Dods said “construction destroys top soils and plant material” so beginning a new project requires restoring site soils so native plants can take root again. Also, “erosion is the enemy of stormwater management best practice,” largely because metals stick to sediment. The goal then is to reduce the movement of soils so you capture sediment that has absorbed metal particulates.
3. Site characteristics inform design. Schuessler noted that soil types and levels of compaction below ground will obviously have impact on how successful an ecological stormwater management system is.
4. Size is important. Properly sized sites can maximize stormwater capture and pollutant removal while saving money.
5. Distribute systems. There shouldn’t be one failure zone.
6. Diversify. “Divere systems are resilient. Nature is diverse,” said Dods. In this case, diversity relates to plant species as well. If one plant type dies, the system can still function.
7. Plant material is important. “Match plants to moisture zones,” argued Schuesller. Test plants to see what kind of ecological function they provide.
8. Keep designs simple to get the best results.
9. Low-cost designs can be effective.
10. Make the landscape beautiful so people want to be there and learn how these systems actually work.
Image credit: ASLA 2011 Student Awards General Design Honor. Co-Modification Joseph Kubik, Student ASLA, Graduate, University of Pennsylvania
Faculty Advisor: Mark Thomann